Pro-active Management of Beet Armyworm (Spodoptera
exigua) Resistance to the IGRs, Tebufenozide and
Methoxyfenozide
John K. Moulton, David A. Pepper, & Timothy J. Dennehy
Extension Arthropod Resistance Management Laboratory
Department of Entomology, University of Arizona
Abstract
Susceptibility to tebufenozide and methoxyfenozide of beet armyworm
(Spodoptera exigua) from the southern United States and Thailand was
determined through exposure of first and third instar larvae to dipped cotton
leaves. LC50 estimates of first instar larvae ranged from 0.377 to 32.7
micrograms of tebufenozide per milliliter and 0.034 to 11.5 micrograms of
methoxyfenozide per milliliter. LC50 estimates of third instar larvae ranged
from 4.37 to 715 micrograms of tebufenozide per milliliter and 0.393 to 47.4
micrograms of methoxyfenozide per milliliter. These estimates translated into
87-fold and 164-fold decreases in susceptibility to tebufenozide and 338-fold
and 121-fold decreases in susceptibility to methoxyfenozide of first and third
instar larvae from a Thailand strain when compared to the most susceptible of
eight United States populations evaluated. Among the United States field
populations evaluated, a collection from Belle Glade, Florida was the most
susceptible and one taken near Parker, Arizona was the least susceptible.
Selection of the Thailand population with tebufenozide or methoxyfenozide
resulted in significant reductions in susceptibility to both analogs, indicating a
common mechanism of resistance. Isolation and characterization of resistance
will provide information that will be helpful for pro-active management of
resistance for this valuable group of insecticides in the United States.
Introduction
During the past 15 years, a new class of insect growth regulators emerged from the discovery that substituted
dibenzoyl hydrazines, or biasacylhydrazines, act as agonists of 20-hydroxyecdysone (Wing 1988, Wing et al.
1988). Acute doses induce a prompt cessation of feeding followed by eventual death through induction of a
premature larval molt (Wing et al. 1988; Rohm & Haas Company 1989; Smagghe & Degheele 1994a, b). Chronic
doses have a chemosterilizing effect by disrupting both oogenesis and spermatogenesis (Smagghe & Degheele
1994a, b). Signs of acute poisoning include, but are not limited to, double head capsule formation, blackening of
the cuticle, stunted growth, extrusion of the hindgut, and loss of hemolymph. The primary route of entry is
ingestion.
The sentinel member of this chemical class was discovered by Rohm and Haas Company scientists in 1983 (Hsu
1991). A more potent analog, RH-5849, was discovered later that same year. RH-5849 showed insecticidal
activity against certain Lepidoptera, Diptera, and Coleoptera pest species but was not developed commercially
due to discoveries of more potent and selective analogs. Most of the early physiological and toxicological studies
on the biasacylhydrazines were performed with this compound.
This is a part of The University of Arizona College of Agriculture 2000 Vegetable Report, index
at http://ag.arizona.edu/pubs/crops/az1177/
Tebufenozide (RH-5992) was discovered in 1986. It was found to be much more potent against and selective
towards larval Lepidoptera than was RH-5849 (Carlson et al. 1994; Dhadialla et al. 1998). Under the trade names
Confirm®, Mimic®, and Romdan®, it is now widely used in several crops throughout the world. The first uses of
tebufenozide in the United States occurred in Alabama and Mississippi in 1994 under Section 18 exemptions.
Section 18 exemptions have since been granted for specific crop uses in North Carolina, Georgia, Florida,
Mississippi, Louisiana, Texas, New Mexico, California, and Arizona. It currently has Section 3 (full) registrations
in the United States for use in cotton, cole crops, leafy vegetables, fruiting vegetables, turnip, cranberries, sugar
cane, pecan, and walnut.
Methoxyfenozide, or RH-2485, was discovered in 1990 and is the latest compound in this class to be developed
commercially. First announced in 1996, it is the most potent analog to date against larval Lepidoptera (Ishaaya et
al. 1995, Trisyono & Chippendale 1997, Le et al. 1996). The first sales of methoxyfenozide, as
Intrepid®/Runner®, occurred in 1999 (R. K. Jansson, personal communication). First registration of
methoxyfenozide in the United States is slated to occur in cotton and pome fruits during 2000 (R. K. Jansson,
personal communication).
The widely distributed, polyphagous pest, Spodoptera exigua, is one of the major targets for development of
tebufenozide and methoxyfenozide in agriculture. Coinciding with the first uses of tebufenozide in Thailand and
new registrations in the United States, we initiated a pro-active resistance management program aimed at
sustaining the efficacy of this class of chemistry. Complementary building blocks of this resistance management
program are the determination of baseline susceptibilities to tebufenozide and methoxyfenozide of field and
laboratory reference populations, routine monitoring of susceptibility, and selection, isolation, and
characterization of resistance. Isolation of resistance to novel compounds like tebufenozide and methoxyfenozide
allows critical practical information to be collected thereafter regarding cross-resistance, genetics and stability of
resistance, and the underlying physiological mechanism(s) of resistance.
In January 1996 we began receiving eggs of beet armyworm from several regions in Thailand, three years after
use of tebufenozide had commenced in that country. From 1996-1997, a total of ten Thailand populations were
evaluated for susceptibility to tebufenozide. Two of these populations displayed significant reductions in
susceptibility to tebufenozide in diet incorporation bioassays (JKM, DAP, and TJD, unpublished observations).
In this paper we present data on the baseline susceptibility of Spodoptera exigua to tebufenozide and
methoxyfenozide and results from laboratory selection of a Thailand strain exhibiting reduced susceptibility to
both compounds. It comprises the first of a series of increasingly more in-depth investigations aimed towards
providing a better understanding of this resistance. Ultimately, we hope these data will provide insight that will
aid in sustaining the efficacy of these valuable new compounds against beet armyworm.
Materials and Methods
Cultures
Field populations were established from samples collected by members of our laboratory and Rohm and Haas
Company. Arizona field populations were established from larvae collected from cotton, brought to the Extension
Arthropod Resistance Management Laboratory (EARML) in Tucson, AZ, and placed onto artificial diet (Heliothis
Premix, Stonefly Industries, Bryan, TX) to complete development. Field populations from elsewhere were
shipped to EARML as surface sterilized eggs under the terms of USDA-APHIS permit number 39094, and the
resulting neonates were allowed to complete development by placing them on the aforementioned artificial diet.
The susceptible reference strain was established from eggs shipped to EARML from the USDA-Western Cotton
Research Laboratory (WCRL) in Phoenix, AZ.
Rearing
All cultures of Spodoptera exigua larvae were reared on Stonefly Industry's Heliothis Premix diet, to which was
added 5 ml of formalin and 1.5 g of aureomycin (chlortetracycline HCL, Fort Dodge Animal Health, Fort Dodge,
IA) to each 2000 g of prepared diet (500 g diet, 1500 ml water) to prevent pathogen growth. Forty to fifty
neonates were placed into 5.5 oz plastic cups and incubated at 27°C (16 h photoperiod). Pupae were collected
from these cups after 14-21 days and placed into one gallon glass jars with wire mesh lids for adult emergence.
Adults were provided 10% sucrose solution and wax paper sheets on which to oviposit. Egg sheets were collected
daily, washed in 10% formalin for 10 min., and rinsed in tap water for 10 min.
Leaf-dip Bioassays
First instar larvae. Fully expanded, first true leaves of 2-3 week old cotton plants were dipped for 5 sec. in
deionized water solutions containing tebufenozide or methoxyfenozide and 0.01% surfactant (Latron CS-7, Rohm
& Haas Co., Philadelphia, PA). Ten replicates were established for each of six to seven concentrations, plus a
control (surfactant only). After drying, one leaf each was placed into 1 oz plastic cups containing 10 ml of
solidified 2% agar solution. Ten neonates were placed into each plastic cup and incubated at 27°C (16 h
photoperiod) for 120 h. Missing and dead larvae were scored as affected. Larvae were scored as dead if no
movement was observed after their having been prodded with a dissecting needle. Bioassay data were analyzed
using probit analysis (POLO-PC) (LeOra 1987).
Third instar larvae. Leaves were selected and dipped as detailed above in the assay of first instar larvae. Ten to
twenty replicates were established for each of six to seven concentrations, plus a control (surfactant only). After
drying, pairs of leaves were placed into 100 x 15 mm Petri plates. Two to three ca. 1.5 cm (5-7 day old) third
instar larvae were then placed into each Petri plate. The Petri plates were subsequently sealed inside one-gallon
plastic zipper bags, each containing a damp paper towel, and incubated at 27°C (16 h photoperiod) for 96 h.
Larvae were scored as dead if they exhibited noticeably blackened or malformed cuticle, including a double or
slipped head capsule. Missing larvae were not scored. Bioassay data were analyzed using probit analysis (POLOPC) (LeOra 1987).
Incorporation of Tebufenozide and Methoxyfenozide into Diet
Pre-mixed wettable powder formulations of tebufenozide and methoxyfenozide were obtained from Rohm & Haas
Company. These formulations were then further diluted into Heliothis Premix diet to obtain mixtures that, upon
the addition of three parts water, would yield treated diet ranging in concentration from 0.3 to 320 µg
tebufenozide or methoxyfenozide/ml. Some of this treated diet was used to select for increased resistance in the
Thailand strain.
Selection for Resistance
The Thailand strain was initially selected on diet containing 10 µg/ml tebufenozide. Approximately 300 third
instar larvae were placed individually into 1 oz plastic cups containing approximately 10 ml of treated diet and
incubated at 27°C (16 hr. photoperiod) for 96 h. Survivors were transferred into 5.5 oz plastic cups containing
untreated diet and allowed to complete development. Progeny of survivors were bioassayed as detailed above to
estimate susceptibility to both compounds. The resulting colony was subsequently divided into two strains that
were subjected to different selection pressures. One was pressured with 30 µg/ml tebufenozide in diet (= Confirmselected #1) and again with 78 µg/ml tebufenozide in diet (= Confirm-selected #2). The other was pressured with
10 µg/ml methoxyfenozide in diet (= Intrepid-selected #1). Subsequent generations were not pressured.
Results
Susceptibility to tebufenozide in leaf-dip bioassays
First instar larvae. LC50 estimates ranged from 0.377 µg/ml for Florida (Belle Glade 2) to 32.7 µg/ml for
Thailand (Intrepid-selected #1) (Table 1). LC90 values ranged from 1.13 µg/ml for Florida (Belle Glade 2) to 101
µg/ml for Thailand (Intrepid-selected #1) (Table 2). Based upon comparisons of LC50 and LC90 estimates, the
Intrepid-selected Thailand strain was 44- to 68-fold less susceptible than the reference strain (Tables 1, 2).
The Florida (Belle Glade 2) strain was the most susceptible to tebufenozide of the U.S. field populations
evaluated. In fact, this population was twice as susceptible as the reference strain at the LC50, although their 95%
confidence limits overlap slightly at the low end. The Arizona (Parker) strain was the least susceptible U.S. field
population evaluated, having LC50 and LC90 estimates of 1.63 and 7.76 µg/ml, respectively. These values were 4.3
and 6.9-fold greater than those of the most susceptible field populations evaluated.
The non-selected Thailand strain exhibited LC50 and LC90 values of 4.41 and 16.9 µg tebufenozide/ml. These
values were approximately twice those of the least susceptible U.S. field population, Arizona (Parker). After
selection of the Thailand strain with 10 µg tebufenozide/ml diet and 10 µg methoxyfenozide/ml diet, tebufenozide
LC50 and LC90 values increased to 32.7 and 101 µg/ml, a 6- to 7-fold further reduction in susceptibility.
Third instar larvae. LC50 values ranged from 4.37 µg/ml for the South Carolina strain to 715 µg/ml for Thailand
(Intrepid-selected #1) (Table 1). LC90 values ranged from 7.06 µg/ml for the USDA reference strain to 10,500 µg/ml
for Thailand (Intrepid-selected #1) (Table 3). Thailand (Intrepid-selected #1) was 150- to 1500-fold less susceptible
to tebufenozide than the reference strain (Tables 3, 4).
The Arizona (Parker) strain, with LC50 and LC90 estimates of 12.0 and 29.6 µg/ml, respectively, was the least
susceptible of the U.S. field strains evaluated. The LC50 value for the Parker strain was significantly different from
those of the other U.S. field strains evaluated. All U.S. field strains, other than Arizona (Parker), were no more than
two-fold less susceptible to tebufenozide than was the reference strain at both the LC50 and LC90 (Tables 3, 4).
After selection of the Thailand strain with 10 µg tebufenozide/ml diet and 78 µg tebufenozide/ml diet, tebufenozide
LC50 and LC90 estimates increased from 46.6 and 147 µg/ml to 127 and 2030 µg/ml. These values corresponded to a
2.7- to 13.8-fold further reduction in susceptibility. After selection of the Thailand strain with 10 µg tebufenozide/ml
diet and 10 µg methoxyfenozide/ml diet, tebufenozide LC50 and LC90 estimates increased from 46.6 and 147 µg/ml to
715 and 10,500 µg/ml. These values corresponded to a 15- to 71-fold further reduction in susceptibility.
Tebufenozide resistance in the Thailand strains declined in the laboratory in the absence of selection pressure. LC50
estimates for third instar larvae from Thailand (Intrepid-selected #1) declined from 715 µg/ml five months post
selection to 351 µg/ml eleven months post selection (Tables 3, 4). LC90 estimates for this strain declined from 10,500
µg/ml to 3,137 µg/ml during this time. Nine months after laboratory colonization, the non-selected Thailand strain
exhibited LC50 and LC90 estimates of 46.6 and 147 µg tebufenozide/ml. These values were 4- to 5-fold greater than
those of the least susceptible U.S. field population evaluated, Arizona (Parker). After 14 months in the laboratory,
LC50 and LC90 values for the non-selected Thailand strain declined to 14.4 and 76.5 µg tebufenozide/ml, only 1.2- and
2.6-fold greater than those observed in Arizona (Parker) (Tables 3, 4).
Methoxyfenozide leaf-dip bioassays
First instar larvae. LC50 values ranged from 0.034 µg/ml for the USDA reference strain to 11.5 µg/ml for Thailand
(Intrepid-selected #1) (Table 5). LC90 values ranged from 0.0631 µg/ml for the USDA reference strain to 20.4 µg/ml
for Thailand (Intrepid-selected #1) (Table 6). These values corresponded to a 320- to 340-fold reduction in
susceptibility of Thailand (Intrepid-selected #1) to methoxyfenozide.
Arizona (Parker), with LC50 and LC90 values of 0.407 and 1.08 µg/ml, respectively, was the least susceptible U.S. field
strain evaluated. Based upon these values, the Arizona (Parker) strain was 3.7 to 7.0-fold less susceptible than the
most susceptible field population evaluated, Florida (Belle Glade 2). Florida (Belle Glade 2) was the only field strain
evaluated that was not significantly different than the reference strain at both the LC50 and LC90.
At the time it was first assayed, the non-selected Thailand strain exhibited LC50 and LC90 values of 0.313 and 1.74 µg
tebufenozide/ml. This LC50 value was less than those observed in the two Arizona strains evaluated. After selection
of the Thailand strain with 10 µg tebufenozide/ml diet and 10 µg methoxyfenozide/ml diet, methoxyfenozide LC50 and
LC90 values increased to 11.5 and 20.4 µg/ml, a 12- to 37-fold further reduction in susceptibility.
Third instar larvae. LC50 values ranged from 0.393 µg/ml for the USDA reference strain to 47.4 µg/ml for Thailand
(Confirm-selected #2) (Table 7). LC90 values ranged from 1.83 µg/ml for Florida (Belle Glade 2) to 169 µg/ml for
Thailand (Intrepid-selected #1) (Table 8). The most highly resistant Thailand strains were 87- to 120-fold less
susceptible to methoxyfenozide than the reference strain (Tables 7, 8).
Arizona (Parker), with LC50 and LC90 values of 2.23 and 5.89 µg/ml, respectively, was the least susceptible U.S. field
strain evaluated. These estimates were 3.7- and 3.2-fold greater than those of the most susceptible field populations.
The South Carolina and Arizona (Parker) strains were the only ones that differed significantly from the reference
strain at the LC50. All U.S. field strains, other than Arizona (Parker) were no more than 5-fold less susceptible to
methoxyfenozide than the reference strain (Tables 7, 8).
LC50 and LC90 values for the non-selected Thailand population were 3.83 and 14.1 µg methoxyfenozide/ml, only 0.6
and 2.4 times that observed in the Arizona (Parker) strain. After selection of the Thailand strain with 10 µg
tebufenozide/ml diet and 78 µg tebufenozide/ml diet, methoxyfenozide LC50 and LC90 values increased to 47.4 and
130 µg/ml, a 9.2- to 12.4-fold further reduction in susceptibility. After selection of the Thailand strain with 10 µg
tebufenozide/ml diet and 10 µg methoxyfenozide/ml diet, methoxyfenozide LC50 and LC90 values increased to 23.5
and 169 µg/ml, a 6.1 to 12-fold further reduction in susceptibility.
Discussion
A Thailand population of beet armyworm collected from the Bangbuathong District, Thailand, an intensive
vegetable production area near Bangkok, has been confirmed to be highly resistant to tebufenozide and
methoxyfenozide. Susceptibility to tebufenozide of this Thailand population compared to that of the laboratory
reference strain, as inferred from leaf-dip bioassays, ranged from 44- to 68-fold for first instar larvae to 150- to
1500-fold for third instar larvae. For methoxyfenozide, these resistance ratios were 320- to 340-fold and 87- to
120-fold, respectively.
Selection of the Thailand population with either analog significantly increased resistance to both, indicating at
least some level of cross-resistance. The Thailand strain selected with methoxyfenozide was somewhat more
resistant to both compounds than was the one selected entirely with tebufenozide. However, because the
Intrepid®-selected strain was initially selected with tebufenozide, it is not possible to discern whether there are
some differences in mechanisms of resistance to these analogs or whether the greater toxicity of methoxyfenozide
resulted in more effective amplification of resistance. Experiments are currently underway to distinguish between
these hypotheses.
This report is the first of tebufenozide and methoxyfenozide resistance in beet armyworm, or any species of
Spodoptera. Smagghe et al. (1998) were able to decrease susceptibility to tebufenozide of a laboratory strain of
beet armyworm after continuous pressuring of larvae for ten consecutive generations on treated diet. However,
the shift in susceptibility they observed was only 5- to 10-fold at the LC50 and LC90, and no significant shifts were
observed until the sixth generation. They also found that piperonyl butoxide synergized tebufenozide activity in
this laboratory strain when both compounds were incorporated into the diet. Synergism ratios were 3.4-fold for
the non-selected strain and 6-fold for the tenth and eleventh generations of the selected strain. In a similar study,
Smagghe and Degheele (1997) were unable to reduce susceptibility to tebufenozide of a laboratory strain of cotton
leafworm, Spodoptera littoralis, by more than 4- to 5-fold after more than one dozen continuous generations of
selection.
The Arizona (Parker) strain was the least susceptible U.S. field strain evaluated. It had the highest LC90 estimates
in first and third instar larvae leaf-dip assays of both analogs and the highest LC50 estimates in assays of both
analogs against third instar larvae. Compared to the most susceptible field population, resistance ratios for the
Arizona (Parker) population ranged from 2.7-7.1 for all assays conducted. Selection of this Arizona strain in a
manner similar to that used for the Thailand strain is currently underway and will hopefully shed light on the
mechanism attributable for its decreased sensitivity to these compounds. Because tebufenozide now has Section 3
registrations in cotton and vegetables, it is of vital interest that we carefully monitor sensitivity to it and
methoxyfenozide in the intensive vegetable/cotton production system of southwestern Arizona.
Many insecticides, including the benzoylureas, chlorfluazuron (Atabron®), triflumuron (Alsystin®), and
teflubenzuron (Nomolt®), have been rendered ineffective in the Bangbuathong District of Thailand due to illadvised agricultural practices, most notably dilution of insecticide residues on leaves by drench irrigation
(Wirojchewan Tawatchai, in. litt.). This practice is likely to blame for the high incidence of insecticide resistance
development in this area and the highly accelerated rate of tebufenozide resistance development in beet
armyworm. The first signs of tebufenozide resistance occurred there after only three years of use and by the
fourth year tebufenozide had been rendered completely ineffective.
We cannot be certain that our findings of tebufenozide and methoxyfenozide resistance in Thailand reflect the
eventual path that evolution will take in other populations of beet armyworm around the world. Similarly, we
cannot be certain that the reduced susceptibilities we observed in some domestic U.S. populations are
representative of the potential for or earliest stages of resistance development to these compounds. However, with
the isolation of the strains described herein, we now have the ability to test these and related questions, the results
of which will improve our ability to react to beet armyworm resistance, once it occurs in Arizona, and help sustain
this valuable new technology. Lastly, our findings of resistance to tebufenozide and methoxyfenozide in Thailand
should serve as a warning of the need to steward this extremely valuable new class of insecticides.
Acknowledgments
We thank R. K. Jansson and G. R. Carlson of Rohm and Haas for their continued financial support of this project.
T. S. Dhadialla, R. Hunter, and T. Duttle, also of Rohm & Haas, are thanked for providing logistical and technical
support. D. E. Kelley (Rohm & Haas Co.) provided the Thailand strain. T. J. Henneberry and the USDA-Western
Cotton Research Laboratory provided the laboratory strain and furnished insights about beet armyworm rearing.
W. D. Nielson (EARML) assisted with rearing and bioassay set-up. M. E. Wigert (EARML) and M. A. Sims
(EARML) are thanked for managing the EARML greenhouses, from which cotton plants for bioassays were
provided.
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Table 1. Probit regression analysis of responses of first instar BAW larvae to tebufenozide in leaf-dip bioassays.
LC50s expressed as µg tebufenozide/milliliter. Resistance ratios based upon comparisons to USDA-WCRL strain.
Population
n
Slope
LC50 (95% FL)
RR
USDA-WCRL
700
4.19
0.736 (0.419-0.969)
1.0
Florida-Belle Glade2
600
2.69
0.377 (0.233-0.503)
0.51
Florida-Belle Glade1
790
1.77
1.34 (0.828-1.96)
1.8
S. Carolina
700
1.94
1.29 (0.778-1.79)
1.8
AZ-Parker
780
1.89
1.63 (0.663-2.61)
2.2
Mississippi
800
2.37
1.59 (0.950-2.25)
2.2
AZ-Maricopa
700
3.27
1.80 (1.35-2.21)
2.4
Thailand (non-selected)
690
2.20
4.41 (3.01-5.81)
6.0
Thailand (INT-sel.#1)
800
2.62
32.7 (18.0-44.6)
44
Table 2. Probit regression analysis of responses of first instar BAW larvae to tebufenozide in leaf-dip bioassays.
LC90s expressed as µg tebufenozide/milliliter. Resistance ratios based upon comparisons to USDA-WCRL strain.
Population
n
Slope
LC90 (95% FL)
RR
USDA-WCRL
700
4.19
1.49 (1.11-3.67)
1.0
Florida-Belle Glade2
600
2.69
1.13 (0.870-1.64)
0.76
AZ-Maricopa
700
3.27
4.42 (3.52-6.25)
3.0
Mississippi
800
2.37
5.51 (3.78-10.7)
3.7
S. Carolina
700
1.94
5.90 (4.16-10.7)
4.0
Florida-Belle Glade1
790
1.77
7.11 (4.62-13.3)
4.8
AZ-Parker
780
1.89
7.76 (4.85-19.2)
5.2
Thailand (non-selected)
690
2.20
16.9 (12.7-25.1)
11
Thailand (INT-sel.#1)
800
2.62
101 (71.9-218)
68
Table 3. Probit regression analysis of responses of third instar BAW larvae to tebufenozide in leaf-dip bioassays.
LC50s expressed as µg tebufenozide/milliliter. Resistance ratios based upon comparisons to USDA-WCRL strain.
"A" and "B" are results from assays conducted on Intrepid-selected Thailand strain five and 11 months,
respectively, after second round of selection. "C" and "D" are results from assays conducted on non-selected
Thailand strain 9 and 14 months, respectively, after its colonization in the laboratory.
Population
n
Slope
LC50 (95% FL)
RR
USDA-WCRL
509
7.39
4.73 (3.97-5.32)
1.0
S. Carolina
484
3.57
4.37 (3.29-5.24)
0.92
Florida-Belle Glade2
280
5.72
4.45 (3.23-5.14)
0.94
AZ-Maricopa
346
2.84
4.58 (2.28-6.36)
0.97
Florida-Belle Glade1
368
3.54
5.65 (3.72-6.94)
1.2
Mississippi
210
3.85
6.39 (4.78-7.72)
1.4
AZ-Parker
374
3.27
12.0 (9.74-14.5)
2.5
Thailand (non-selected)D
227
1.77
14.4 (10.0-21.0)
3.0
Thailand (non-selected)C
164
2.57
46.6 (31.2-67.2)
9.9
Thailand (CONF-sel.#2)
604
1.10
127 (60.7-218)
27
Thailand (INT-sel.#1)B
232
1.35
351 (219-516)
74
Thailand (INT-sel.#1)A
160
1.10
715 (366-1280)
150
Table 4. Probit regression analysis of responses of third instar BAW larvae to tebufenozide in leaf-dip bioassays.
LC90s expressed as µg tebufenozide/milliliter. Resistance ratios based upon comparisons to USDA-WCRL strain.
"A" and "B" represent results from assays conducted on Intrepid-selected Thailand strain five and 11 months,
respectively, after second round of selection. "C" and "D" are results from assays conducted on non-selected
Thailand strain 9 and 14 months, respectively, after being placed in the laboratory.
Population
n
Slope
LC90 (95% FL)
RR
USDA-WCRL
509
7.39
7.06 (6.29-8.37)
1.0
Florida-Belle Glade2
280
5.72
7.45 (6.59-9.32)
1.1
S. Carolina
484
3.57
9.98 (8.32-13.2)
1.4
AZ-Maricopa
346
2.84
12.9 (9.46-24.3)
1.8
Florida-Belle Glade1
368
3.54
13.0 (10.9-18.1)
1.8
Mississippi
210
3.85
13.8 (11.3-18.9)
2.0
AZ-Parker
374
3.27
29.6 (23.1-43.9)
4.2
Thailand (non-selected)D
227
1.77
76.5 (74.4-156)
11
Thailand (non-selected)C
164
2.57
147 (95.8-321)
21
Thailand (CONF-sel.#2)
604
1.10
2030 (1198-4120)
290
Thailand (INT-sel.#1)B
232
1.35
3137 (1895-6884)
440
Thailand (INT-sel.#1)A
160
1.10
10500 (5080-32700)
1500
Table 5. Probit regression analysis of responses of first instar BAW larvae to methoxyfenozide in leaf-dip
bioassays. LC50s expressed as µg methoxyfenozide/milliliter. Resistance ratios based upon comparisons to USDAWCRL strain.
Population
n
Slope
LC50 (95% FL)
RR
USDA-WCRL
700
4.76
0.034 (0.019-0.042)
1.0
Florida-Belle Glade2
700
1.83
0.058 (0.025-0.096)
1.7
S. Carolina
700
3.15
0.149 (0.119-0.182)
4.4
Mississippi
700
4.39
0.218 (0.150-0.263)
6.4
Florida-Belle Glade1
500
2.41
0.303 (0.185-0.419)
8.9
Thailand (non-selected)
700
1.72
0.313 (0.125-0.519)
9.2
AZ-Parker
700
3.02
0.407 (0.286-0.518)
12
AZ-Maricopa
600
4.28
0.487 (0.385-0.583)
14
Thailand (CONF-sel.#2)
700
1.73
2.53 (1.50-3.66)
74
Thailand (INT-sel.#1)
700
5.14
11.5 (8.79-14.0)
340
Table 6. Probit regression analysis of responses of first instar BAW larvae to methoxyfenozide in leaf-dip
bioassays. LC90s expressed as µg methoxyfenozide/milliliter. Resistance ratios based upon comparisons to USDAWCRL strain.
Population
n
Slope
LC90 (95% FL)
RR
USDA-WCRL
700
4.76
0.0631 (0.053-0.082)
1.0
Florida-Belle Glade2
700
1.83
0.290 (0.181-0.572
4.6
S. Carolina
700
3.15
0.380 (0.300-0.528)
6.0
Mississippi
700
4.39
0.427 (0.353-0.628)
6.8
AZ-Maricopa
600
4.28
0.971 (0.808-1.25)
15
Florida-Belle Glade1
500
2.41
1.03 (0.750-1.64)
16
AZ-Parker
700
3.02
1.08 (0.849-1.55)
17
Thailand (non-selected)
700
1.72
1.74 (1.14-3.05)
28
Thailand (CONF-sel.#2)
700
1.73
13.9 (9.66-23.3)
220
Thailand (INT-sel.#1)
700
5.14
20.4 (16.3-33.4)
320
Table 7. Probit regression analysis of responses of third instar BAW larvae to methoxyfenozide in leaf-dip
bioassays. LC50s expressed as µg methoxyfenozide/milliliter. Resistance ratios based upon comparisons to USDAWCRL strain.
Population
n
Slope
LC50 (95% FL)
RR
USDA-WCRL
359
1.85
0.393 (0.211-0.592)
1.0
Mississippi
188
1.72
0.601 (0.409-0.866)
1.5
Florida-Belle Glade2
280
2.67
0.605 (0.420-0.800)
1.5
Florida-Belle Glade1
181
2.11
0.656 (0.463-0.919)
1.7
AZ-Maricopa
148
2.02
0.935 (0.272-1.78)
2.4
S. Carolina
180
4.09
1.80 (1.18-2.36)
4.6
AZ-Parker
196
3.04
2.23 (1.17-3.29)
5.7
Thailand (non-selected)
240
2.26
3.83 (2.25-5.54)
9.8
Thailand (INT-sel.#1)
681
1.50
23.5 (16.5-31.2)
60
Thailand (CONF-sel.#2)
200
2.94
47.4 (29.7-62.4)
120
Table 8. Probit regression analysis of responses of third instar BAW larvae to methoxyfenozide in leaf-dip
bioassays. LC90s expressed as µg methoxyfenozide/milliliter. Resistance ratios based upon comparisons to USDAWCRL strain.
Population
n
Slope
LC90 (95% FL)
RR
USDA-WCRL
359
1.85
1.94 (1.33-3.29)
1.0
Florida-Belle Glade2
280
2.67
1.83 (1.33-3.09)
0.94
Florida-Belle Glade1
181
2.11
2.65 (1.74-5.12)
1.4
Mississippi
188
1.72
3.35 (2.10-6.83)
1.7
S. Carolina
180
4.09
3.71 (2.79-6.79)
1.9
AZ-Maricopa
148
2.02
4.04 (2.13-12.6)
2.1
AZ-Parker
196
3.04
5.89 (3.95-13.2)
3.0
Thailand (non-selected)
240
2.26
14.1 (9.57-26.7)
7.3
Thailand (CONF-sel.#2)
200
2.94
130 (93.0-284)
67
Thailand (INT-sel.#1)
681
1.5
169 (122-266)
87